Multistate proteomics analysis reveals novel strategies used by a hibernator to precondition the heart and conserve ATP for winter heterothermy

Abstract

SL. Multistate proteomics analysis reveals novel strategies used by a hibernator to precondition the heart and conserve ATP for winter heterothermy. Physiol Genomics 43: 1263-1275. First published September 13, 2011 doi:10.1152/physiolgenomics.00125.2011.-The hibernator's heart functions continuously and avoids damage across the wide temperature range of winter heterothermy. To define the molecular basis of this phenotype, we quantified proteomic changes in the 13-lined ground squirrel heart among eight distinct physiological states encompassing the hibernator's year. Unsupervised clustering revealed a prominent seasonal separation between the summer homeotherms and winter heterotherms, whereas within-season state separation was limited. Further, animals torpid in the fall were intermediate to summer and winter, consistent with the transitional nature of this phase. A seasonal analysis revealed that the relative abundances of protein spots were mainly winter-increased. The winter-elevated proteins were involved in fatty acid catabolism and protein folding, whereas the winter-depleted proteins included those that degrade branched-chain amino acids. To identify further statedependent changes, protein spots were re-evaluated with respect to specific physiological state, confirming the predominance of seasonal differences. Additionally, chaperone and heat shock proteins increased in winter, including HSPA4, HSPB6, and HSP90AB1, which have known roles in protecting against ischemia-reperfusion injury and apoptosis. The most significant and greatest fold change observed was a disappearance of phospho-cofilin 2 at low body temperature, likely a strategy to preserve ATP. The robust summer-to-winter seasonal proteomic shift implies that a winter-protected state is orchestrated before prolonged torpor ensues. Additionally, the general preservation of the proteome during winter hibernation and an increase of stress response proteins, together with dephosphorylation of cofilin 2, highlight the importance of ATP-conserving mechanisms for winter cardioprotection. 2D DiGE; CFL2; hibernating; Ictidomys (spermophilus) tridecemlineatus; mass spectrometry HIBERNATION IN MAMMALS IS characterized by dramatic, but reversible, reductions in body temperature (T b ) and metabolic rate. During this torpid phase, respiration and heart rate also decline to 1-4% of their euthermic values (for review, see Ref. 11). Torpor bouts are punctuated by interbout arousals (54), when physiological rates are restored to or even surpass euthermic levels (11). For circannual hibernators such as 13-lined ground squirrels, Ictidomys tridecemlineatus, the ability to orchestrate reversible metabolic depression exists only in winter (reviewed in Ref. 38). This heterothermic winter phenotype contrasts markedly with summer, when animals remain homeotherms. A "two-switch" mechanism in which animals first switch from summer homeothermy to a state that is permissive for winter heterothermy (switch 1), and then cycle between periods of torpor and arousal in winte...

Gene expression changes controlling distinct adaptations in the heart and skeletal muscle of a hibernating mammal

“…This is consistent with previous findings of reduced expression of proteins associated with mitochondrial ␤-oxidation of branched chain fatty acids (34).…”

Metabolic Flexibility: Hibernation, Torpor, and Estivation

“…Cofilin 2 (CFL2) is specific to muscle and regulates the turnover of actin filaments. Grabek et al (122) found that phosphorylated CFL2 was virtually undetectable in torpor and early arousal, and at very low levels during entrance. During IBE, and indeed euthermia at any time of the year, phosphorylated CFL2 was quite abundant, and the total amount of CFL2 did not change throughout the year.…”

“…Many proteomic changes occur in the heart of 13-lined ground squirrels over the course of the year. Though most of these changes are related to seasonal transitions at least one difference among phases of a torpor bout stands out with potential to conserve metabolic energy (122). Cofilin 2 (CFL2) is specific to muscle and regulates the turnover of actin filaments.…”

Proteomic Mechanisms of Cardioprotection during Mammalian Hibernation in Woodchucks, Marmota Monax

“…In contrast, Martin et al used the two-dimensional differential gel electrophoresis (DIGE) approach to identify protein differences in intestines of ground squirrels ( Ictidomys tridecemlineatus ) between sham-treated animals with those exposed to ischemia-reperfusion (I/R) 10 ; these proteomics profiles of intestines were able to distinguish among the sham-treated summer and hibernating samples, as well as I/R-induced proteomic changes between summer and hibernating animals. More recently Grabek et al discovered the importance of proteins involved in ATP-conserving mechanisms for winter cardioprotection in the hearts of 13-lined ground squirrels 11 . In the present study, we conducted two independent sets of iTRAQ quantitative proteomics experiments in order to discover hibernation and DT-specific cardiac proteomic changes in Marmota monax ; summer animals were served as the controls in each set of experiments; the first set involved non-hibernating winter animals fed and housed at room temperature and the summer control animals, and the second set involved winter animals in DT and the summer control animals.…”